1. Field of the Invention
The present invention relates to devices for preheating internal combustion engine exhaust gases before the gases reach the catalytic converter during and shortly after a cold engine start. More particularly, the present invention relates to a catalytic converter heater having a simplified structure and improved performance.
2. Description of the Prior Art
The exhaust system of internal combustion engines include a catalytic converter which uses a catalytic reaction to reduce harmful pollutants of the exhaust gas, including hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO.sub.x) before the exhaust gas reaches the atmosphere. However, the catalyst in the catalytic converter will react with the exhaust gas so as to properly remove pollutants therefrom only after it has attained a minimum "light-off" temperature, typically in the range between 350 and 450 degrees Centigrade. Following the initial phase of engine operation, the exhaust gas will supply sufficient heat to maintain the catalyst above the light-off temperature. However, during the initial phase of engine operation, defined as the time period between a cold start and the catalyst reaching the light-off temperature, the exhaust gas is insufficiently hot to raise the catalyst to the light-off temperature. The initial phase of engine operation can be in the range of 75 to 100 or more seconds, depending on the ambient temperature, design of the engine, and driving conditions. Accordingly, during the initial phase of engine operation, harmful pollutants of the exhaust gases may be released to the atmosphere.
In order to minimize release of harmful pollutants of the exhaust gas to the atmosphere during the initial period of engine operation, it is desirable to raise the temperature of the catalyst as quickly as possible to the light-off temperature. Since the exhaust gas during the initial phase of engine operation has insufficient heat for this purpose, a secondary source of heat must be introduced into the catalytic converter.
There are two basic technologies for providing supplemental heat to a catalytic converter during the initial phase of engine operation. One technology uses an electrical heater for heating internal members of the catalytic converter. This system requires a large electrical power drain on the electrical system of the internal combustion engine in order that sufficient heat be delivered in a small time period. The other technology uses a burner located in the exhaust system upstream of the catalytic converter to thereby augment the temperature of the exhaust gases entering into the catalytic converter. This system uses the fuel of the internal combustion engine as its source of fuel. Burner systems are favored (although not universally, of course) over electrical systems because they deliver higher levels of heat with greater efficiency.
An example of a catalytic converter heater operating on the burner principle is described in U.S. Pat. No. 5,339,630, which is assigned to the assignee hereof.
In the catalytic converter heater described in the aforementioned patent, a combustor head assembly is provided having means for mixing fuel and air, and a source of ignition is provided for the fuel and air mixture. A charge preparation assembly within the combustor head comprises a two-stage vortex which cooperates with a fuel nozzle to atomize the fuel and combine it with air to thereby produce a fuel and air mist. The fuel and air mist is subsequently injected into a combustor including an elongated tubular combustor chamber having the combustion head assembly at a first end and a series of louver or round outlets, placed circumferentially at its opposite end to promote mixing of the burner output with the exhaust gases from the internal combustion engine.
The combustor is mounted within a burner housing. An interlocking flange assembly retains the combustor and the burner together as a single unit. Exhaust gas enters the housing through an inlet adjacent to the combustor outlets such that exhaust gas entering the burner housing passes over the exterior of the combustor and past the louvered outlets to maximize heat retrieval. Dilution air, which may be required to complete combustion of the burner fuel and to assure maximum conversion efficiencies in the catalytic converter during the initial phase of engine operation, is added to the exhaust gas at a location upstream of the combustor so as to encourage mixing of the dilution air with the exhaust gas prior to heating by the burner.
The burner assembly is operably connected, preferably integrally with the exhaust system, to a catalytic converter with the exit lying in close or adjacent proximity to the inlet of the converter, in order to reduce the size of the assembly and limit heat loss between the burner and the catalytic converter.
While the hereinabove described catalytic converter heater serves to provide heating of the exhaust gases of an internal combustion engine, there still remains a need in the art to provide a catalytic converter heater which is of simplified construction, thereby providing the benefits of reduced weight, size, cost and manufacturing complexity, while yet providing optimal operational characteristics. Still needed in the art, too, is a catalytic converter heater which is structured for being universally installable with any exhaust system.